Dk 3.48 against 3.38, Tg above 280°C and a CTE matched to copper: the numbers behind RO4350B and RO4003C, and what they change in a design.
RO4000 series laminates are hydrocarbon ceramic materials built to deliver high-frequency performance at a fabrication cost closer to FR-4. The two grades most often specified are RO4350B, with a dielectric constant of 3.48, and RO4003C, with a dielectric constant of 3.38. Both are low-loss, and both run on standard epoxy and glass processes — which is the whole point of the series. The wider family is introduced in our Rogers RO4000 series overview.
As operating frequencies move past 500 MHz and beyond, the range of substrates that remain usable narrows quickly. RO4000 materials supply what RF and microwave circuits need: a stable dielectric constant, low dielectric loss, and the predictability that controlled impedance transmission lines and matching networks depend on.
Two properties make them comfortable in broadband work. The temperature coefficient of the dielectric constant is among the lowest of any circuit board material, and the value holds over a wide frequency range, so a design verified in one band does not drift out of specification in another. Where insertion loss needs to come down further, LoPro foil is available as an option.
The two grades differ in dielectric constant by 0.10, which is a meaningful difference when impedance and line width are being fixed. Everything else in the table is common ground.
| Parameter | RO4350B | RO4003C |
|---|---|---|
| Dielectric constant (Dk) | 3.48 | 3.38 |
| Dielectric loss | Low | Low |
| Dk tolerance | Tight | Tight |
| Glass transition temperature (Tg) | above 280°C (536°F) | above 280°C (536°F) |
| Coefficient of thermal expansion | Similar to copper; low Z-axis | Similar to copper; low Z-axis |
| Through-hole preparation | Standard FR-4 process, no sodium etching | Standard FR-4 process, no sodium etching |
| Flame rating | UL 94V-0, RoHS-compliant | RoHS-compliant |
| Specification | IPC-4103 | IPC-4103, slash sheet 10 |
The coefficient of thermal expansion of RO4000 materials sits close to that of copper, and that single fact produces several design benefits at once. Dimensional stability through thermal cycling is the first: it is what allows mixed-dielectric multilayer structures to keep their registration rather than shearing as the assembly heats and cools.
The second is through-hole integrity. A low Z-axis CTE keeps plated through-holes reliable even under severe thermal shock, because the barrel moves less than it would in a material with a larger vertical expansion. With a Tg above 280°C (536°F), these extended properties hold across the whole circuit processing temperature range.
RO4000 laminates fabricate using standard FR-4 techniques. Unlike high-performance PTFE-based materials, they do not require specialised through-hole preparation such as sodium etching, and because they are rigid thermoset laminates they move through automated handling systems and copper surface scrubbing equipment without special provisions. That compatibility is what keeps the cost competitive — the practical consequences for design and fabrication are covered in our RO4350B applications and fabrication guide, with additional material detail in the RO4350B material overview.
RO4003C laminates are manufactured using 1080 and 1674 glass fabric styles, with every configuration meeting the same laminate electrical performance specification. RO4350B was designed as a direct replacement for RO4003C, using RoHS-compliant flame-retardant technology that meets UL 94V-0 requirements. Both materials comply with IPC-4103, with RO4003C classified as slash sheet 10.
The feature list separates into three groups:
The applications follow from the property set — broadband performance, low loss and FR-4-like processing:
Where the design needs a lower dielectric constant than the RO4000 series provides, the PTFE-based options covered in our RT/duroid 4003C advantages article are the next comparison to run.
Common questions about RO4350B and RO4003C parameters.
RO4350B is specified at 3.48 and RO4003C at 3.38. Both are low-loss hydrocarbon ceramic laminates with tight Dk tolerance, and both can be fabricated on standard epoxy and glass processes.
Above that point the choice of usable substrates narrows sharply. A stable Dk with a low temperature coefficient keeps impedance and signal behaviour predictable across a wide frequency range, which is what broadband and controlled-impedance designs depend on.
No, and that is their main commercial advantage. They are rigid thermoset laminates that run on standard FR-4 processes and do not need specialised through-hole preparation such as sodium etching, unlike PTFE-based high-performance materials.
A coefficient of thermal expansion close to copper gives dimensional stability through thermal cycling, which matters for mixed-dielectric multilayer structures, and the low Z-axis CTE keeps plated through-holes reliable under severe thermal shock.
Satellite TV LNBs, cellular base station antennas and power amplifiers, RFID tags, automotive radar and sensors, and microstrip lines — broadband work where low loss and FR-4-like processing are both required.
Send us the frequency range, impedance targets and layer count. We will compare the two grades against your stack-up and quote the build with the Dk that gives the cleaner design.
Get A Recommendation → Fast Reply on WhatsApp